Ductile acrylonitrile copolymers



Patented Dec. 9, 1952 BUC'IILE ACRYLONITRILE COPOLYMERS Fred W. Banes,Westfield, and John D. Garber,

Cranford, N. J., assignors to Standard Oil Development Company, acorporation of Delaware No Drawing. Application December 29, 1947,Serial No. 794,434

6 Claims.

This invention relates to snythetic polymers, and more particularly to amethod for preparing fiber-forming co-polymers from a monooefin and anacrylic compound.

Fibers from polyacrylonitrile and from copolymers containing a majorproportion of combined acrylonitrile and a minor proportion of anothercomonomer such as isobutylene and various special methods of preparingsuch fibers from solutions have been known heretofore. It has also beenknown that synthetic fibers could be prepared from polyamide typepolymers or from adipic acid hexamethylene diamine condensation productsby simple melt extrusion. However, heretofore the art has been incapableof producing resinous polymers of high nitrile content which could beformed into fibers by melt extrusion, either because polymers of highnitrile content prepared according to previously known processes weretoo high melting to allow of direct melt extrusion, and/or because theydarkened and became otherwise physically inferior when heated topractical extrusion temperatures.

Prior to the present invention, the only practical method of formingfibers from macrom-olecular polymers containing a majo porportion ofcombined acryl'onitrile involved the dissolving of such polymers inspecial nitrogen-containing solvents such as dimethyl formamide,dimethylmethoxy-acetamide, N-formyl morpholine, N- formyl hexamethyleneimine, tetramethylene cyclic sulfone, l, 2, 3-trithiocyanopropane, gammathiocyanobutyronitrile, and a few other uncommon solvents. This methodis essentially described in U. S. Patent No. 2,404,713, but as isapparent from the character of the solvents which are rare, expensiveand often poisonous, the process puts these otherwise highly desirableresins at a serious economical disadvantage as compared with resinscapable of being drawn into fibers by melt extrusion, which lattermethod is particularly desirable since it involves no problem of solventrecovery.

It is an object of this invention to provide the art with macromolecularsolid polymers of high nitrile content which can be melt extruded anddrawn to form exceptionally strong and otherwise highly-valuable fiberspossessing a high degree of molecular orientation. A more specificobjectof our, invention is to prepare acrylonitrileisobutylenecopolymers which are very tough and hard, but which may be readilyextruded at moderately elevated temperatures and drawn into flexible,grease-resistant, fairly shrink-proof filaments of superior tensilestrength. Other objects will become apparent from the subsequentdescription.

A new method has now been discovered whereby macro-molecular resinouscopolymers of high nitrile content may. be prepared in such a novel formthat they can be melt extruded at temperatures between about280 F. and400 F. and drawn into strong, flexible fibers, thereby beingdistinguishable from and superior to related polymers such as thosedescribed in British Patent 573,086, which can not be formed into highlyoriented fibers by extrusion and drawing.

According to this invention, the nitrile copolymers are modified duringtheir polymerization so that a required amount of copolymer is made upof what is believed to be bound sulphur in the form of thioetherradicals. For example, in order to obtain polymers which can be readilyextruded and drawn into flexible fibers at temperatures below 400 F. andbelow the decomposition or degradation point of, the polymers, it wasfound necessary to incorporate 0.05 to 1.5 or even 3% of thioethersulphur, which is equivalent to about 0.1 to 10% of thioether radicals,into the polymer structure, the most preferred amount depending onpolymerization conditions, chemical structure of the nitrile and itsco-monomer, and proportion of combined nitrile in the desired polymer.

Furthermore, while it is recognized that unmodified nitrile polymershave been previously dissolvedand extruded in solution by well-known wetor dry spinning processes wherein the polymer is coagulated by suitablechemicals or by heat, it has been found new that the mercaptan-modifiedpolymers of this invention are superior to the unmodified polymers ofthe prior art, even for fiber formation from solutions because themodified polymers are more readily soluble, so that even the oldspinning processes can be made more economical.

In practicing the instant invntion, an iso-alkene having 4 to 8 carbonatoms per molecule such as iso-amylene, 2, 4, 4 trimethyl pentene-l, orpreferably isobutene is copolymerized in aqueous emulsion with anacrylic-nitrile such as acrylonitrile, methacrylonitrile,ethacrylonitrlle, alphachlor-acrylonitrile, or other similar nitriles ormixtures thereof having the formula CH2 2 CY.C E N wherein Y may beselected from the group consisting of hydrogen, methyl, ethyl andchlorine. Copolymers of particularly excellent extrusion properties canbe prepared from monomer feeds having a weight ratio of 25-85 parts ofacrylonitrile to 75-15 parts of isobutene, which monomer feeds givepolymers having a combined acrylonitrile content varying from 62 to 85weight percent (as determined by nitrogen analysis).

In general, copolymers having an lsobutene content higher than 38%extrude with particular ease. but have poorer shrinkage and solventresistance characteristics than copolymers having an isobutene contentless than 38%. However, besides the chemical composition, theprocessability and other properties of the copolymers depend upon theirmolecular weight and other variables which will be discussedsubsequently.

For instance, the present invention is applicable to the preparation ofcopolymers of somewhat different properties which can be obtained byreplacing the iso-olefin or iso-alkene of the charge by normal alkenesran ing from 2 to 5 carbon atoms per molecule such as ethylene, n-buteneand n-pentene: or cyclic olefins such as cyclopentene, cyclohexene orpreferably vinyl cyclohexene; or olefins substituted with one to threehalogen atoms such as dichloroet y ene, trichlomethylene, allyl chlorideand methallyl chloride. Furthermore, the nitrile of the charge may bereplaced in part or in its entirety by amides of maleic, fumaric,itaconic, crotonic, methacrylic or other unsaturated acid.

The method of preparing the new extrudable copolymers is carried out byemulsifying the organic monomers in an aqueous medium, the weight ratioof monomers to water being from about 2:1 to about 1:4 or even 1:10,ratios be tween 1:2 and 1:4 being especially preferred where the monomerfeed contains more than 85 weight percent acrylonitrile to weightpercent of isobutene.

Furthermore, it is necessary to have the hydrogen ion concentration at apH value between about 10.5 to 6.5 or lower, and preferably at a pHvalue within the range of 7 to 9. This can be accomplished convenientlyby the addition to the water of sodium bicarbonate, or alkalihydroxides, carbonates or bicarbonates generally. Alternatively, pHvalues lower than 6.5 are also operative down to a pH of about 3 wheresuch high hydrogen ion concentration is due to the presence of weakacids, especially organic acids such as formic, acetic, oxalic, citricor the like. However, if such high acidity of the aqueous polymerizationmedium is due to the presence of strong mineral acids, notablysulphuric, the resulting polymer is unduly tough and cannot normally bedrawn or extruded satisfactorily and with emulsifiers of the typerepresented by Emulphor ON the polymerization will not proceed at allunder these conditions of high acidity. Conversely, copolymers preparedin systems having a pH higher than about 10.5 are also tough andunsatisfactory for extrusion, though this deleterious effect of highalkalinity can often be compensated at least in part by addingespecially 'large amounts of mercaptan modifier to the poly- -merizationcharge, whereby the molecular weight '4 of the resulting copolymer isreduced and the processability thereof improved.

The aqueous portion of the reaction charge should also contain about 2to 8 or more weight percent (based on combined monomers) of anemulsifier, high emulsifier concentrations being especially recommended.where the formation of stable latices is desired from a monomericmixture containing more than about weight percent of acrylonitrile, andless than 15 weight percent of isoalkene. With monomer feeds containingless than 85 weight percent of acrylonitrile, excellent copolymers canbe prepared when the aqueous portion of the charge contains 3 to 5weight percent of a synthetic detergent type emulsifier exemplified bythe formula RSO3M wherein R is selected from the group consisting ofalkoxy radicals having 8 to 18 carbon atoms, alkyl radicals having 12 to30 carbon atoms and of alkyl substituted phenyl or naphthyl radicalshaving 12 to 30 aliphatic carbon atoms in the alkyl substituent, andwherein M is an alkali metal ion such as sodium or potassium or anammonium radical. In other words, the detergent emulsifier may be analkyl sulfate such as potassium octyl sulfate CsHrIOSOzK, sodium laurylsulfate C12H25O.SO3Na, sodium cetyl sulfate C16H330.SO3N2, or ammoniumoctadecyl sulfate C1sHa7O.SO3NH4; or it may be an alkyl sulfonate suchas potassium dodecyl sulfonate C12H25.SO3K, or sodium tricontylsulfonate or it may be an alkyl aromatic sulfate such as the sodium saltof dodecyl benzene sulfonic acid.

Of the aforementioned types of emulsifiers the alkyl sodium sulfateshaving 12 to 16 carbon atoms such as the sodium lauryl sulfate soldcommercially as an aqueous paste containing 33 weight percent of thesulfate (Orvus), or sodium cetyl sulfate have been found particularlyfavor able to the course of the desired reaction.

Still other types of useful emulsifiers are those obtained by thecondensation of alcohols or phenols with ethylene oxide, such as theproduct commercialy known as Emulphor ON and obtained by thecondensation of oleyl alcohol with ethylene oxide. This last mentionedemulsifier may be used to produce copolymers well adapted for extrusioninto good fibers, but the polymerization yields are somewhat lower thanwith the aforementioned preferred emulsifiers.

On the other hand, copolymers prepared in the presence of ordinary fattyacid soaps such as the ordinary alkali stearates or oleates or rosinacid soaps such as the Dresinates or soaps derived from tallow acids,are diiiicult to extrude unless exceptionally large amounts of mercaptanmodifier are added to the polymerization mixtiu'e so as to reduce themolecular weight of the resulting copolymer considerably below thevalues ordinarily considered satisfactory for the extrusion ofcopolymers prepared in the presence of the preferred emulsifiers.

It may be observed that high emulsifier concentrations tend to favor theformation of copolymers of lower intrinsic viscosity and therefore ofsomewhat better processability than copolymers prepared in systems oflow emulsifier content. Accordingly, it will be apparent that theemulsifier concentration need not be limited to the range suggestedhereinbefore, but may be gredi'ents, the: waterphase; also contains:about 0.3 to 2 or 5weight percent (based onmonomers) of a peroxide typecatalyst exemplified by the water-soluble persulfates or pereorates ofsodium, potassium or of ammonium. The yield is increased slightly byincreasing the catalyst concentration, whereby also an improvement of.processing characteristics is obtained because of a concomitantdecreasein intrinsic viscosity. However, balancing the desire to have an easilyprocessable polymer with the desire to obtain a fiber of optimumphysical and chemical properties, concentrations of about.0.5 to 0.75weight percent of sodium persuliate or potassium .persulfate have beenvfound most advantageous.

Finally it is essential to have present in. the reactionmixture analiphatic. mercaptanhaving at. leastfour andpreferably eight to eighteencarbon atoms per molecule. A particularly effective. modifier was foundin a commercial mixture ofv primary mercaptans derived from thecorresponding mixture of alcoholsof cocoanut oil origin. Thiscommercial. mercaptan mixture was found to have the followingcomposition as determined by distillation at 5 mm. Hg:

Percent Lower than 01 o Lower than 0 Lower than C C13 and higher Fromthe above analysis it will be seen that the mercaptan mixture consistspredominantly of a major proportion of lauryl mercaptan (C12) and aminor proportion of tetradecyl mercaptain (C14) Accordingly, whenever amixture of primary C12 to C 14 mercaptans is referred to in thesubsequent description and claims, it will be understood that the morecomplex mixture defined above is meant. However, other primarymercaptans such as butyl, hexyl, heptyl, and so forth, through hexadecylmercaptan, are also useful, are the tertiary mercaptans. Among thelatter, t-octyl mercaptan has been found to be especially desirable,being more effective than either t-heptyl or t-dodecyl mercaptans. Theamount of mercaptans used should be between about 0.2 and weight percentbased on the monomers but the preferred amount necessarily depends onseveral factors, i. e. acrylonitrile content of feed, type and amount ofemulsifier, relative acidity of aqueous phase, reaction temperature, andfinal properties desired.

The presence of such mercaptan modifiers accelerates the reaction rateand stabilizes the resulting latex so that the reaction mixture ispreserved in the reactor as a stableand homogeneous dispersion. Thispermits the eventual addition of such materials as stabilizers and otheringredients to the vented latex in such a fashion that the addedingredients become uniformly dispersed therein prior to coagulation andsubsequent polymer finishing operations, whereby the uniformity andgeneral quality of the product is improved significantly.

However, the most remarkable result of the addition of the mercaptan tothe polymerization charge is that by such addition the normal course ofthe polymerization becomes so modified that the resulting product iscapable of extrusion in the form of strong fibers whereas analogous:products polymerized in the'vabsenceof mercaptans.-

cannot be extruded or drawn. This modification or internalpiasticization of thepolymeric products. is especially surprising sinceheretofore thev of the action of the mercaptans in the present inventionis strikingly illustrated by the factthat butyl mercaptan has been foundto bequite effective as a modifier whereas mercaptans having less than 6carbon atoms have been known heretofore exclusively as polymerizationpoisons and even have been used deliberately as short-stopping agents.

After the aqueous and polymerizable portions and the mercaptan of thecharge have been admixed in the reaction vessel, vapors of the volatileingredients are allowed to escape for a few minutes in order to flushthe system free of oxygen. The reaction vessel is then sealed and placedon a shaking or agitating device either in a constant temperature bathor in an electrical heating jacket. The reaction mixture is thus heatedat temperatures of 25-70 C. for a period of time ranging from 5 tohours. Usually, polymerizations have been run at about 40 C. to 60 C.for a period of 10 to 18 hours as illustrated in subsequent examples.

Furthermore, we have found that the homogeneity can be improved stillfurther by adding the more reactive monomer such as the acryloni-' trilecontinuously or portionwise, instead of all at once. Thereby themechanical strength and also the transparency of the product are furtherimproved somewhat.

At the end of the polymerization the reactor is removed from theagitating device, vented and the latex poured into a receiver. A shortstop agent such as hydroquinone, hydroxylamine hydrochloride and/orother customary processing ingredients may then be added to the latexand coagulation effected in a known manner by means of sodium chloridebrine and/or alcohol or the like. The resulting coagulated resinouspolymer is then in the form of fine crums which can be washed with waterto remove the emulsifier, water-soluble catalyst, etc. and the purifiedpolymer can then be dried in any suitable known manner, e. g. on trays,in an oven or on a hot mill. prior to further operations.

Examples illustrative of this method of polymerization are given below:

EXAMPLE I Solutions containing 400 grams of water, 27 grams of anaqueous dispersion containing 33 weight percent of sodium lauryl sulfate(Orvus Paste) and 1.5 grams of potassium persulfate were charged to aglass-lined, one-liter reactor after the pl-I of the final solution hadbeen raised to 8.5 by addition of 0.6 gram of sodium bicarbonate to eachcharge. The desired amount of a commercial mixture of C12 to C1mercaptans (Lorol), prepared from the corresponding commercial mixtureof alcohols consisting mostly of lauryl alcohol, was then added to thereactor, followed by quantities of acrylonitrile and of isobutyleneindicated in the subl'oined Table I. The reactors were flushed withisobutylene vapors, sealed and placed on a revolving wheel in aconst'anttemperature bath where they were agitated for 17.5 hours at 50 C. Themaximum autogenous pressure during each of the runs was of the order of100 pounds per square inch. At the end of this time the reactors werecooled to room temperature and their contents of latex poured into2-liter vessels. No coagulum or gel was present in these latices andupon addition of sodium chloride brine the polymer coagulated from thelatices in fine crumb form. These coagulates were thoroughly washed withwarm water to remove all emulsifier and persulfate catalyst and thenthey were dried in a vacuum oven for about eight hours at about 80 C.The dried polymers were thereafter weighed and tested, the results beingsummarized in Table I below:

Table I POLYMER A B C D Monomer feed (gms.):

Acrylonitrile 50 80 100 160 Isobutylene 150 120 100 40 Cir-C14 mercaptan(gins 1.0 1. 1. 55 4.2 Polymer yield (gms). 67 105 130 l86 Conversion(Derccnt) 38.5 52.5 65 93 Polymer analysis:

Percent nitrogen "16.45 17.10 18.19 20.10 Percent acrylonitrlle(calculated). 62.3 64.8 69. 0 76. 2 Percent sulphur 0.10 Percentthioether radicals (calculated) Intrinsic viscosity I 0. 50 Extrusiontemperature (F.) 38o Monofil diam. (mm) 0. 0.10 Tensile (p. s. i. X 7555 50 32 Percent shrinkage in straight-run mineral spirits having aboiling range of 150- 200 (1.:

At 75 C 40 40 30 2 At 90 C 95 95 82 9 l Determined from solutionscontaining 0.2 gram of copolymer in 100 cc. of nitrometuane, intrinsicviscosity 1;; being defined by the In 7]r 1 a v1 00511: ManonCOllOOIltl'EltlOl'l whele m1 s y time of hog of solution through acapillary time of how of solvent through same capillary These dataillustrate the properties of fibers prepared from copolymers of Variouscomposition. It will be seen that as the acrylonitrile contents of thepolymeric resins are increased the extrusion temperature must beincreased to obtain smooth, ductile materials. In all of the aboveexamples the polymers could be easily extruded and drawn tosubstantially water white monofilaments of small diameter.

When polymers were prepared with identical charges to those given inTable I except that the mercaptan was omitted, the polymers could not beextruded at temperatures below 400 F. or below their degradationtemperature. As a specific example a polymer was prepared with the samecharge as given in Table I under Polymer. C except that no mercaptan wasadded to the charge. The dry, washed product weighed 125 grams andcontained 18.62% nitrogen (70.6% acrylonitrile) and had an intrinsicviscosity of 1.56. The polymer extruded very slowly at 390 F. to giverough, dark colored rods which could not be drawn to fibers.

EXAIVIPLE II The novelty of our copolymers is further illustrated by thefollowing data which were obtained in two runs, A and B, which wereidentical except that run A was conducted according to the teaching ofBritish Patent 573,086, whereas in run B 1.25 weight percent (onmonomers) of a mixture of C12 to C14 mercaptans (DDM Lorol) has beenadded to the polymerizable mixture according to our invention. Thespecific data. and results follow.

One hundred grams of acrylonitrile and grams of isobutylene were addedto a one-liter reactor (A) containing 6.0 grams of sodium cetyl sulfate(95% purity) as an 8.0% aqueous solution, 0.5 gram of sodiumbicarbonate, 2.0 grams of ammonium persulfate and 322 grams of water.The same charge was placed in a similar second reactor (B) and inaddition 2.5 grams of a mixture of 012 to C14 primary mercaptans(prepared from a mixture of the corresponding alcohols) was added to thesecond reactor. The additions of the various components were carried outin th manner prescribed in the above-mentioned patent and thepolymerization was carried out for 137 hours at 25 C. with agitation ina constant temperature water bath. At the end of 137 hours the reactorswere removed from the bath, discharged, and the latices coagulated, thecoagulate washed and dried in a manner identical to that disclosed inthe aforementioned patent. The following data were obtained on thefinished polymers:

Table II Polymer Yield of polymer (parts by weight) Percent conversion(on monomers) Percent nitrogen in polymer spirits having a boiling rangeof 200 C. at 75 C.

These data illustrate that a polymer prepared according to the methoddescribed in British Patent 573,086 cannot be extruded to give fiberswhereas the material of this invention gives very satisfactory fibers.

EXAMPLE IH A series of polymers were prepared with identical chargesexcept that the type of emulsifying agent was different in each case.The charges for the various runs are given in the following Table III.In addition, data are given pertinent to the yields, composition, andextrusion properties of the final product. It will be observed thatallryl sulfates, alkyl sulfonates and alkyl aromatic sulfates gaveeasily extrudable polymers whereas fatty acid and rosin acid soaps gavepolymers with very poor extrusion characteristics.

A polymer was also prepared with the same emulsifier and general recipeas given in run No. G except that the mercaptan content of the chargewas increased from 1.60 to 2.52 grams per 200 grams of monomers. Thefinal polymer weighed 121 grams, contained 17.31% nitrogen (65.7%acrylonitrile) and had an intrinsic viscosity of 0.68. However, in spiteof this low viscosity this product like the one prepared with lessmercaptan could not be extruded at 380 F. with out obtaining rough,dark-colored rods incapable of being drawn to fibers.

Table III Charge:

100 g. Acrylonitrile 100 g. Isobutyleue 1.5 g. X28208 1.6 g. Lorolmercaptan 400 g. water 10.0 g. emulsifier 17.5 hours at 50 (3.

I Percent Type of Emulsifier Emulsifier 23%? 3g, Extrusion not 1Paraffinic sulfate (Na salt) A Orvus (so ium lauryl sulfate). 122 70. 0.76 Good. Petroleum hydrocarbon... B 0) 130 68. 0 82 Do. Sulfonate (Nasalt) C 112 66.0 .84 Do. Ethylene oxide-alcoho1 (or phenol) co D 95 72.0.88 Fair. Alkyl aromatic sulfonate (Na salt) E 122 69. 5 .76 Good. Rosinacid soaps (Na salt) F 94 71.3 1.09 Very poor. Fatty acid soaps (Nasalt) G Hvfirogeugtcd tallow acids or 126 65. 4 .725 Poor.

0 cream 1 Combined acrylonitrile content calculated irom nitrogenanalysis.

2 Run in nitromethane in cone. of 0.20 g./l00 ml. solvent. 1Dehydroabietic acids.

EXAMPLE D7 The effect of reaction time and temperature was studied incomparative runs wherein .80 parts of acrylonitrile and 50 parts ofisobutene were copo'lymerized according to this invention as an aqueousemulsion in the presence of 4.5 parts sodium lauryl sulfate, 0.84 partof amixtu-re of C12 to C14 mercaptans (Lorol) 0.75 part of potassiumpersulfate and 200 parts water, the parts being These results showclearly that the more elevated polymerization temperature is moreadvantageous because of the substantially shorter reaction timesrequired for attaining; the same conversion as that obtained at thelower temperature. Furthermore, the copolymers prepared at 50 C. have alower intrinsic viscosity, and hence better extrusion characteristics,than copolymers of the same yield and same combined acr'ylonitrilecontent but prepared at C. Conversely, to obtain copolymers extrudablewith the same degree of ease a larger proportion of mercaptan modifiermust b present in the feed when the copolymer is prepared at a lowertemperature than when a copolymer of the same combined acrylonitrilecontent is prepared at a more elevated temperature.

EXAMPLE V A study was made of the relations between acrylonitrilecontent of feed (and copolymer), mercaptan content of charges, intrinsicviscosity, and extrudability of the copolymers. The polymerizations werecarried out in glass-lined, oneliter reactors according to the techniquedevscribed in the previous example, except that the following specificconditions were employed:

Charge: Grams Isobutylene plus acrylonitrile in feed 200 Water 400Sodium lauryl sulfate-" 9.0 Potassium persulfate 1.5

C12 to C14 mercaptan mixture Variabl pH (adjusted with NaI-ICOa) 8.2Temperature (C.) 50 Reaction time .(hours) 17.5

Table V Acrvloni- Con- Acrylomtnle/ trile-in isobutylene versioncopolymer. I-ntmmc Extrudabilit (weight ratio) 35 (weig s; S0os1ty ypercen 50 65-68 0.60 Excellent. 62. 68-70 .62 Do. 74 ll-73 65 Good. 8472-76 64 Fair. 92 76-80 .65 Poor. 97 -85 63 Do.

1 Calculated from nitrogen content of copolymer. 9 Determined fromsolutlons containing 0.2 gram of copolymer in 100 cc. of mtromethane.

It is apparent from the above results that when the amount of mercaptanwas kept constant and the acrylonitrile-isobutylene.ratio was varied,all other conditions being the same, the molecular weight as determinedin terms of intrinsic viscosity of the resulting copolymers wasessentially constant. However, it is significant to note that althoughthe intrinsicviscosity of the several copolymers was very nearlyconstant, the ease of extrusion became noticeably poorer as the nitrilecontent of the copolymers increased.

However, from a large number of similar polymerizations it wasdetermined that very good extrusion characteristics can be obtained evenin the case of copolymers having a high nitrile con- I 1 tent if theamount of mercaptan modifier present in the polymerization charge isincreased corre- 12 produced therefrom are summarized in the m1- lowingtable:

spondingly. As a result of evaluation of a large Charge: Gms number ofcopolymers prepared according to the Acrylonitrfle 10o recipe given inthe first part of this example but 5 lsobutylene 100 in the presence ofdifierent mercaptan concensodium lauryl lf t (added in the formtrations, it has been determined that the eX- 127 gmgoforvuspaste) 9trudability, acrylonitrile content, mercaptan c 1 Potassium persulfate1.5 centration of charge and intrinsic viscosity of the 10 Water 400copolymers prepared under the given conditions Polymerization: 17.5hours at 50 C.

Table VI Run A B o D E Sodium Method of pH adjustment ggg ggg bicartbon-Sodium hydroxide Lorol mercaptan (gm.) 1. 9 1. 9 l. 9 1. 2 1.9 1. 9

Polymer yield (gm.) 120 120 124 119 122 116 Percentnitrogen 18.57 18.3618.11 18.41 18.34 18.48

Percent acrylonitril 70. 5 69. 6 68. 7 69. 8 69. 5 70 2 Int. vis 0. 84O. 98 0.75 1. 4 0. 95 1. 50

Extrudability and ductility Good Poor Good Very poor Fair Very poor havean interrelation which is shown by the data summarized in Table V-A:

Table V-A Minimum parts of Cir-C14 mercaptan mixture required to giveextruCable polymers (weight percent on monomers) Maximum intrinsicviscosity for good extrusion and drawing to fibersAcrylonitrile/isobutylene (weight ratio in feed) llllll From the abovedata, the relation of acrylonitrile concentration to the'minimum amountof mercaptan necessary in the polymerization mixture to give asatisfactorily extrudable polymer is established by the followinglogarithmic equation 66.4 log S=C'-60, or by the equivalent exponentialequation EXAMPLE VI A series of polymers were prepared with an identicalcharge in each instance except that the pH of the aqueous portion of thecharge was varied over the range of 3.35 to 11.5. Data regarding thepolymerizations and the polymers These data indicate that polymersprepared in aqueous solutions whose pH has been lowered with weakorganic acids were easily extruded whereas polymers prepared insolutions whose pH had been lowered with mineral acids were ditficult toextrude or draw to fibers. Polymers prepared in solutions of pH of 10.5or over were likewise difficult to extrude. The data also shows that asthe pH of the aqueous medium was increased beyond a pH of 8.2, thepolymers were more difficult to extrude. However, as the mercaptancontents of the highly alkaline pH systems were increased the resultingpolymers were more extrudable and were quite similar to polymersprepared in the preferred pH range of '7 to 9.

EXAMPLE VII Several runs were performed to illustrate the ability ofacrylonitrile to copolymerize in the presence of mercaptans witholefinic hydrocarbons other than isobutylene. The polymerizations werecarried out in one-liter reactors in the general manner described indetail in several of the preceding examples. Table VII shows the dataobtained in these runs, the specific recipe used here being as follows:

Charge:

Acrylonitrile g 100 Olefinic comonomer g 100 Sodium lauryl sulfate g 3.3Water g 400 Potassium persulfate g 2.0 Commercial 012-014 mercaptan g1.6 Sodium bicarbonate g 0. Reaction temperature C 50 Table VII ReactionPercent Comonomer time Yield (g) AN 111 (hrs.) polymer 1 Iso butylene 18124 69. 5 utcne-l 18 86 Do so 10s as Butene-Z 60 78 90.4 Trimethylethylene 18 78 80 Do e0 84 76.6 Isobutylene dimer 60 110 79. 2 Butadienedimer 60 85. 7

1 Acrylonitrile content calculated from nitrogen analysis.

2 Mixture of 80% 2,4,4 trimethyl pcntcne-l and 20% of 2,4,4 trimetliylpentene-Z.

3 Vinyl cyclohexene.

Of the polymers listed in Table VII, the isobutylene copolymer wassuperior to all others in its ability to form fibers by the extrusionmethod. All of the polymers listed are worthy of note in showing thatthe newly invented method makes possible the preparation ofacrylonitrile copolymers containing substantial amounts of combinedolefin. Trimethylethylene and the isobutylene dimer are seen to beparticularly adapted to copolymerize with acrylonitrile to formcopolymers -of or'more of combined olefin.

EXAMPLE VIII Two sets of runs were made according to the presentinvention in order to illustrate the ef- 1 ficacy of various mercaptansas modifiers. The polymerizations were again carried out in the generalmanner previously described. The specific recipe in the set of runsnumbered 1-12 was as follows:

further substantiate the results shown in Table V as to the minimumamount of mercaptan for 70/30 feed mixtures of acrylonitrile withisobutylene. Runs 5 and 6 illustrate the results achieved by replacing amajor portion of (112-014 mercaptan with a tertiary C8 mercaptan('diisobutylene mercaptan). The results indicate that this mercaptan isat least as effective as the (112-614 mercaptan.

Runs 7-1'1 give the e'fiect of tertiary 'dode'cyl and tertiary heptylmercaptans. A comparison of polymer viscositie's obtained in these runswith the intrinsic viscosity of the mercaptan-free polymer of run 12shows that either of these 5 tertiary polymers exerts a pronouncedmodifying 'efiect on the polymerization, though only about one half orone third as effective on 'a mole basis as the (312-014 mercaptan usedin runs 1-4. Hence, for aliphatic mercaptans of 4-16 carbon atomsgenerally the relation derived from Table V establishing the approximateminimum amount Char e:

icrylonitrfle 70 of mercaptan assuring the formationo'fextrudlsobutylene 30 able polymers must be rewritten in the form ofSodium lauryl sulfate g 4.3 0-6 Sodium bicarbonate g 0.3 3 0662; Water g2 00 'M.W. Potassmm Persulfate wherein S is the minimum number of mole fMercaptan: Varied in type and amounts as indicated in Table VIII.Polymerization: 17.5 hours at 50 C.

The recipe used in the set of runs numbered 13-17 was as follows:

mercaptan necessary per 100 grams of total monomers, M. W.-is themolecular weight of the mercaptan and C is the weight in grams ofacrylic nitrile per 100 grams of totalmonomers. It will be understood,or course, that this equation will give more than the'necessar-y minimumin the Charge: p I 0 case of especially efiective rnerca-ptans such asAcrylomtnle g 0 the C12-C 4 mercaptan mixture or the tertiaryIsobutylene 4 0 3 mercaptan. However, the use of more than sodtumlalurylSulfat? the bare minimum is not detrimental nd ei blcamnate man sunfurther improves the processability g: er. "i 0 75 40 of t e polymer asshown inrun's 1-4.

0 assmm persu a e The results of runs 13-17, wherein a acrylo-Mercaptan: As indicated in Table VIII. Polymerization: 17.5 hours at C.

The data obtained from these runs are summarized in subjoined TableVIII.

nitrilezisobutylene ratio of 50-50 was employed, are self-explanatoryand show that the butyl mercaptan is also an efiective modifier.

From all of these runs it is interesting to note Table VIII Mercaptanadded per 100 g. of monomers 0 AN on- 1 I 1...... Ease Run Amount addedTotal added wsiot germ Sic trusion I cosity' character- Type per per itics Moles Moles cent cent x 10 x 10 9. 2 2 9. 2 87 '74. 7 0.50 Verygood. 5. 83 1. 27 5. 83 80. 5 72. 3 61 GODd. 3. 87 84 3. 37 36 73. 3 76P001. 2. 30 5O 2. 3O 73. O D0. see 3. as 85 72. 7 67 Fair. 1. 0s 6. 7981 72. 6 .48 Very good. 3. 33 671 3. 33 80 72. 9 1. 25 Very D001. 3. 87512 3. 87 83 75. 0 1.12 DO. 93 .897 4. 29 86 7s. 0 .89 Poor. s 1. Z 58762 4. 51 83 74. 3 .90 Do. 633 4. 17 84 74. 0 88 D0. None None None 8073. 3 1. 60 Very poor.

3. 5O 76 3. 50 62 70. 5 76 GOOd. 13. 9 1. 254 13. 9 52 71. 4 82 DO.

6. 63 6. 95 53 70. 0 1. 20 P001. 4. l7 375 4. 97 54 69. 7 l. 31 D0. NoneNone None 60 71.5 1. 58 Very poor.

Combined acrylonitrile content of polymer calculated from nitrogenCommercial mixture of primary (D -C1 mercaptans (average M. respondingmixture of alcohols (Lorol DDM).

Runs 1-4 show the beneficial effect ofincreasing mercaptan concentrationon the extrusion analysis.

W. 217), prepared from corthat the maximum intrinsic viscosity allowablein extrudable polymers prepared according to "characteristics of the'resulting polymers "and 75 the'present invention is criticalan'dsubsta-ntially 15 the same as shown in Table V, regardless of thespecies of mercaptan used.

All of the copolymers disclosed in this specification were evaluated asfiber-forming materials in a small, electrically heated extruder fittedwith a die. The powdered polymeric resin was fed into the extruderbarrel and the temperature adjusted to give a good extrusion rate wherethe material admitted of extrusion at all. All temperature measurementswere made at the extruder head. The extruded rod was stretched bycollecting on a motor driven spool which was rotated at a ratecontrolled to give a fiber of desired diameter. From 5 to spools offiber from each resin were collected at various extrusion temperatures,rates and draw ratios. It is obvious that considerable variation infactors is possible. Average values for extrusion temperature, tensilestrength, shrinkage, etc., were determined.

The fibers were evaluated for tensile strength on 9. Scott microtester(model X-5) which is designed primarily for rubber samples, and hencethe results may not be absolute. However, the data are entirelyreproducible and are on a comparative basis. Shrinkage tests were run byimmersing the fiber for minutes in a bath of straight-run mineralspirits having a boiling range of 150 to 200 C., the bath beingmaintained at 75 -+;fl.2 C.and 90:O.3 C.

In many cases, particularly when the molecular weight of the polymer wastoo high, the polymer extruded as a rough, highly swollen rod. Theseproducts were very difllcult to draw and were considered to beunsatisfactory for the preparation of fibers by extrusion. Severalhundred spools of fiber were prepared and evaluated in this study andrepresentative limiting data are shown in the following table:

about 60/40 which fiber has both an excellent strength, good solventresistance and good shrinkage characteristics or dimensional stability.

The drawing is best accomplished on a motor driven drum or spool. It maybe accomplished in several stages at various temperatures in order toget the desired orientation. By operating at the correct temperature theextruded section can be drawn out to 50, 250 or even 750 times itslength. The fibers may be subjected to an annealing treatment atelevated temperature after stretching in order to improve theirdimensional stability. Dyes, pigments, delustering agents, resins,curing agents and the like may be incorporated into the polymer prior tofiber formation. Or, if desired, the copolymer may be partiallyhydrolyzed or chemically modified and cross-linking effected undertension. The following examples illustrate the extrusion and drawingcharacteristics of our novel polymers.

EXAMPLE IX A mixture of 25 parts of acrylonitrile, 75 parts ofisobutylene and 0.5 part of commercial lauryl (0124314) mercaptan wasemulsified with 200 parts of an aqueous solution containing 4.5 parts ofsodium lauryl sulfate and 0.75 part of potassium persulfate, the pH ofthe aqueous solution having been previously adjusted to a value of 7.8by the addition of sodium bicarbonate, all parts being by Weight. Uponheating this emulsion at 50 C. for 17.5 hours in a closed reactor, acopolymer was recoveredtherefrom containing 38% of bound isobutylene and62% of bound acrylonitrile (as determined by nitrogen analysis). Thiscopolymer was placed on a rubber mill at 310 F. and sheeted 01f after 5minutes mastication as a clear, tough, flexible film. This material wasfed in strips to an extruder equipped TaoZe IX Charge Polymer Org-CPercent linear mercaptan Bound Extrn- Tensile shrinkageAcrylonitrile/iso- (weight Int acrylosion Stmn m 1 in mineral butylenepercent cosit nitrile temper- (lbs g spirits at- (weight ratio) per V151 y (Weight mum in 16 5 monopercent) (F.) mers) 75 C. 90 C.

1 Determined on monofilaments 0.1 mm. in diameter.

The above results show that by proper selection of the ingredients ofthe polymerization charge 'it is possible to extrude copolymerscontaining to 80 weight percent of bound acrylonitrile and to draw theextruded copolymers into resilient fibers of excellent tensile strengthwhich may range from about 10,000 to 100,000 pounds per sq. inch.Furthermore, the above data indicate that by a proper variation of theingredients in the charge within the above limits, it is possible tosynthesize a fiber-forming polymer having the best suited properties forany particular purpose, a high-nitrile copolymer being preferred wherefibers of unusually high solvent resistance are desired while,conversely, a lownitrile copolymer is best where maximum tensilestrength is the primary desideratum. The best all-purpose fiber has beenfound to be the one having a nitrile/isobutylene ratio in the feed ofwith a 3 2-" die and extruded at a rate of about 6 inches per min. atdifferent die plate temperatures and drawn on a spool revolving at about1000 R. P. M. The best extrusion was obtained at about 320 F., at whichtemperature the diameter of the extruded rod was about 1 mm. and thediameter of the drawn fiber or monofil about 0.04 to 0.05 mm.,indicating an extension ratio of about 400 to 600. The average tensilestrength of the monofil was found to be 93,000 lbs. per square inch andits elongation about 60%.

When the same polymer was extruded at tem-- peratures below about 310 F.it was not plastic enough to permit easy drawing, while at extrus'iontemperatures above about 330 F. the extruded rod was found to benoticeably more tender and weak which made its drawing to a fiber quitediificult. This indicates that the extrusion temperature passes throughan easily determinable optimum which will yield the best possible fibersand which will permit the fiberforming operation to proceed mostsatisfactorily.

EXAMPLE X A copolymer was prepared as in Example IX except that theacrylonitrile-isobutylene feed ratio used was 80/20 and the amount ofCir-C14 mercaptan added to the charge was 2.1 percent by weight ofmonomers. The resulting copolymer was found to have 75.3% of combinedacrylonitrile and an intrinsic viscosity of 0.5. This material wasmilled at about 310 F., extruded at 380 to 410 F., and drawn asdescribed in Example IX. The optimum extrusion was obtained at about360-F., at which temperature the diameter of the extruded rod was about1.5 mm. and the diameter of the drawn monofil was about 0.1,

indicating an extension ratio of about 150. The formed monofil wasobserved to be slightly darker in color than the original resin,indicating that slight oxidation took place during the extension step.The tensile strength of the monofil was found to be about 32,000 lbs.per square inch and its elongation about 20 to 40%. A comparison ofthese results with those obtained in Example IX confirms that tensilestrength and extrudabili-ty decrease and optimum extrusion temperatureincreases with increasing nitrile content. However, it is likely thatthese differences in physical properties would be smaller than indicatedby the given absolute figures if in both cases the amount of drawing,that is, the degree of molecular orientation had been carried to thesame extent.

- Finally, when the copolymer of Example X was extruded in a nitrogenatmosphere at temperatures gradually increased to well over 400 F., noserious darkening or degradation occurred showing that the copolymer isinherently stable even at these high temperatures. I

EXAMPLE XI Fibers prepared from isobutylene-acrylonitrile copolymer ofthe present invention and containing60% or more of combinedacrylonitrile were immersed in several different'solvents for threehours at room temperature. Those containing 60% of acrylonitrile becamehighly dispersed in benzene, methyl ethyl ketone and chloroform,

While those containing 70% or more of acrylonitrile were unaffected bybenzene or chloroform and only very slightly swollen in methyl ethylketone. All fibers tested were unaffected by carbon tetrachloride, butall those containing up to 85% of combined acrylonitrile were freelysoluble in nitro-methane, nitroethane, nitropropane, nitrocyclohexaneand their hydroxyl or halogen derivatives. This solubility innitroparafiins of the copolymers of the instant invention can be madeuse of in the formulation of protective coatings. Indeed, for coatingpurposes or for spinning operations it was found that solutions of theinstant copolymers in nitroparaffins such as nitromethane could besuccessfully diluted with varying amounts of thinners such asmethylethyl ketone, carbon tetrachloride, benzene, ethyl acetate and thelike, while isopropyl alcohol, methyl alcohol, diethyl ether and thelike caused precipitation of the copolymer and/or were immiscible withthe solution of copolymer in nitromethane.

Furthermore, we have found that synthetic fibers of the general typedescribed hereinbefore can be subjected to controlled hydrolysis so asto render them exceptionally well suited for fabrics to be used inwearing apparel. It is well known they contain 5, 20 or even of thetheoretical amount of carboxyl groups, the moisture absorption isincreased and fabrics made from extruded fibers of hydrolyzed polymerare warm and soft to the touch, thereby overcoming one of the principalhandicaps that are characteristic of synthetic fibers as compared withnatural ones. Any fiber-forming copolymer containing 50% or more ofbound nitrile may be hydrolyzed, thereby also markedly improving itsdyeing characteristics with basic type dyes.

Hydrolysis of polymers of the above type may be carried out by a caustictreatment of the latex or coagulated or a solution of the polymer ininert solvent.

solutions, by the reaction time and temperature. Hydrolysis to anydesired ratio of -CONH2 to -COOI-I may also be effected.

In addition to modifying the simple copolymers by the hydrolytic methoddescribed, it is also possible to obtain modified copolymers by adding athird or even a fourth copolymerizable substance to the principalmonomeric mixture, thereby obtaiming -p lymers or tetrapolymers ofimproved dimensional stability, softening point and other properties.Among such useful comonomers are: vinyl chloride, vinylidene chloride,methacrylonitrile, vinyl fluoride, dichlorostyrene, vinyl ketones,acrylamide, methacrylamide, chloroacrylonitrile, and the like. In orderto obtain copolymers best suited for fiber formation, we have found itpreferable to polymerize mixtures containing at least 25% but preferably50 parts or more of acrylonitrile, at least 15 and up to 75 parts ofisobutylene and a third comonomer of the class just described, thelatter being present in a proportion not exceeding about 35 to 50 partsper 100 parts of the other two comonomers combined.

Chemical modification by sulfuric acid, nitric acid, halogens,mercaptans, maleic anhydride, phenol and other reagents may be obtained.Use of the above described polymers and their chemical derivatives in.fibers, films, surface coatings, molded objects, rubber and resinplasticizers is indicated. As an example, a tripolymer containing about70% acrylonitrile, 5-10% acrylamide and 20-25% isobutylene may becompounded with formalin, trioxane, dimethylol urea or hexamethylenetetramine and then extruded and drawn to a fiber at a relatively lowtemperature. The fiber may then be subjected to heat, while undertension in either a static or a continuous system, in order to effectcross-liking. Hydrogen chloride, sulfur dioxide, acetic acid or otheracidic compounds may be present in the atmosphere to catalyze thecondensation.

From the foregoing description, it is apparent that we have invented anew method for making novel copolymers which are especially useful inthat they can be extruded and drawn into fibers of excellent properties.It is obvious that many changes and modifications can be made in theabove-described details, without departing from the concept of ourinvention which is not to be limited except as set forth in the appendedclaims.

We claim:

1. In the manufacture of solid copolymers, the improvement comprisingthe steps of mixing 25 to parts by weight of an acrylic nitrile mono-The degree of hydrolysis is 6011-, trolled by the concentration andamount of alkali mer having the formula CH2:CY.CEN wherein Y is anymember of the group consisting of hydrogen, methyl, ethyl and chlorine,with '75 to 15 parts by weight of an iso-alken'e monomer having 4 to 8carbon atoms per molecule, adding to said mixture 0.2 to 5 weightpercent based on said monomers of at least one aliphatic mercaptanhaving 4 to 16 carbon atoms per molecule. the amount of mercaptan withinthe upper part of the given range being used when the amount ofacrylonitrile monomer is in the upper part of its given range; agitatingand emulsifying one volume of the resulting mixture in a closed zone inone-half to four volumes of an aqueous solution having a pH valuebetween 6.5 and 10.5 and containing 3 to 10 weight percent based onmonomers of an emulsifier having the formula R.SO3M wherein M representsa radical selected from the group consisting of alkali metals andammonium and wherein R represents a member of the group consisting ofalkoxy radicals of 8 to 18 carbon atoms, alkyl radicals having 12 to 30carbon atoms and alkyl substituted phenyl and naphthyl radicals having12 to 30 aliphatic carbon atoms, and 0.5 to 1.5 weight percent based onsaid monomers of an alkali persulfate; and heating the resultingemulsion at a temperature within the range of 25 to 7 C. to form a latexof an extrudable resin.

2. In the manufacture of solid copolymers, the improvement comprisingthe steps of mixing 25 to 85 parts by weight of an acrylic nitrilemonomer having the formula CHz:CY.CN wherein Y is any member of thegroup consisting of hydrogen, methyl, ethyl and chlorine, with '75 to 15parts by weight of an alkene monomer having 4 to 8 carbon atoms permolecule, adding to said mixture 0.2 to weight percent based on saidmonomers of at least one aliphatic mercaptan having 4 to 16 carbon atomsper molecule, the amount of mercaptan within the upper part of the givenrange being used when the amount of acrylonitrile monomer is in theupper part of its given range; agitating and emulsifying the resultingmixture in an aqueous solution having-a pH value'between 3 and 10.5 inthe absence of strong mineral acid and containing an emulsifying amountof a compound having the formula R.SO3M wherein M represents a radicalselected from the group consisting of alkali metals and ammonium andwherein R represents a member of the group consisting of alkoxy radicalsof 8 to 18 carbon atoms, alkyl radicals having 12 to 30 carbon atoms andalkyl substituted phenyl and naphthyl radicals having 12 to 30 aliphaticcarbon atoms, and a catalytic amount of a peroxy compound; andpolymerizing the monomers contained in the resulting emulsion by heatingthe said emulsion at a temperature of 25 to 70 C.

3. The method of preparing fiber forming copolymers, comprising theimprovement of mixing 25 to 85 parts by weight of acrylonitrile monomerand 75 to 15 parts by weight of isobutylene monomer, adding to saidmonomers 0.5 to 5 weight percent based on monomers of a mixture ofallphatic mercaptans containing 12 to 14 carbon atoms per molecule,agitating and emulsifying one volume of the resulting mixture in one tofour volumes of an aqueous solution having a-pH value between 7 and 9,said solution containing 3 to weight percent of an alkyl sodium sulfatehaving 12 to 16 carbon atoms per molecule and 0.5 to 1.5 weight percentof an alkali persulfate, and heating the resulting emulsion at atemperature between 40 and 60 C. to form a latex of an extrudable resin,the minimum amount of mercaptan used being determined by theacrylc'nitrile/isobu tylene monomer ratio according to the equation66.4-l0g S:C60, wherein S stands for the minimum parts by weight ofmercaptan to be added per 100 parts of total monomers and wherein 0stands for the parts by weight of acrylonitrile monomer per 100 parts oftotal monomers.

4. An extrudable copolymer containing 65 to weight percent of combinedacrylonitrile and 35 to 15 weight percent of combined isobutylene. 0.05to 3 weight percent of combined sulfur, and having an extrusiontemperature between 300 and 400 F. and an intrinsic viscosity between0.1 and 1, but not higher than determined by the data of the followingtable which shows the maximum allowable polymer viscosity as a functionof said composition:

Maximum intrinsic 5. A fiber of a resinous copolymer soluble innitromethane and containing 65 to 85 weight percent of combinedacrylonitrile, 35 to 15 weight percent of combined isobutylene and 0.05to 3 weight percent of combined sulfur, said fiber being characterizedby a tensile strength of 10,000 to 100,000 lbs. per square inch and saidcopolymer being characterized by an extrusion temperature between 300and 400 F. and by an intrinsic viscosity between 0.1 and 1, but notgreater than that determined by the data of the following table whichshows the maximum allowable polymer viscosity as a function of saidcomposition:

I Maximum Acrylonitrue/isobutylene (weight ratio in feed) intrinsicviscosity 6. An extruded filament of a resinous copolymer containingabout 69 weight percent of combined acrylonitrile, about 31 weightpercent of combined isobutylene and about 0.16 weight percent ofcombined sulfur, said copolymer having an extrusion temperature of about345 F. and an intrinsic viscosity of about 0.78, and said extrudedfilament having a diameter of 0.10 mm.

JOHN D. GARBER. FRED W. BANES.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,396,997 Fryling Mar. 19, 19462,434,054 Roedel Jan. 6, 1948 2,436,926 Jacobson Mar. 2, 1948 2,489,943Wilson et al Nov. 29, 1949 2,531,196 Brubaker Nov. 21, 1950 2,537,146Lytton 1 Jan. 9, 1951 2,537,626 Eberly et a1. Jan. 9, 1951

5. A FIBER OF RESINOUS COPOLYMER SOLUBLE IN NITROMETHANE AND CONTAINING 65 TO 85 WEIGHT PERCENT OF COMBINED ACRYLONITRILE, 35 TO 15 WEIGHT PERCENT OF COMBINED ISOBUTYLENE AND 0.05 TO 3 WEIGHT PERCENT OF COMBINED SULFUR, SAID FIBER BEING CHARACTERIZED BY A TENSILE STRENGTH OF 10,000 TO 100,000 LBS. PER SQUARE INCH AND SAID COPOLYMER BEING CHARACTERIZED BY AN EXTRUSION TEMPERATURE BETWEEN 300 AND 400* F. AND BY AN INTRINSIC VISCOSITY BETWEEN 0.1 AND 1, BUT NOT GREATER THAN THAT DETERMINED BY THE DATA OF THE FOLLOWING TABLE WHICH SHOWS THE MAXIMUM ALLOWABLE POLYMER VISCOSITY AS A FUNCTION OF SAID COMPOSITION: 